The floors are overall in excellent shape, but the ShopVac and I discovered that many pieces are quite loose. I want to glue these back down before refinishing, what would you reccommend? Simple wood glue? Liquid Nails?

Beyond the re-gluing, what would you reccommend for the actual finish? We're not going to stain it, but I've heard about "hardeners" that also bring out the grain? Is this "as seen on TV" or legit? We have a dog that apparently has razor blades for toenails, so it needs to be a pretty tough finish.